1. Technical Field
The present invention relates to display technology that uses electrophoresis of charged particles in a solvent.
2. Related Art
It is generally known that, when an electric field is applied to a dispersion liquid in which charged particles are dispersed in a solvent (dispersion medium), the particles migrate (electrophoretically move) in the dispersion medium by a Coulomb force. This phenomenon is called electrophoresis. Electrophoretic display (EDP) devices that display desired information such as images using the electrophoresis are known.
A known example of such electrophoretic display devices includes a pair of substrates, multiple closed cells formed by dividing a space between the pair of substrates with partition walls, and a dispersion liquid containing charged particles (electrophoretic particles) and dispersion medium enclosed in each of the closed multiple cells. JP-A-2004-4773 and JP-A-2006-162969 describe examples of related art.
Each one of the cells of the EPD can be made to correspond with each of pixels, and a full color display can be achieved by arranging three different colors (for example, red, green and blue) to be correlated with each three of the cells. Such cells may be arranged to have a cell structure, for example, in which (1) white particles, black particles and color dispersion liquid are filled; (2) white particles, black particles and colored particles are filled; or (3) white particles and black particles are filled, and color filters are added.
According to the cell structures (1) and (2) described above, when a red color is to be displayed, the other two (i.e., green and blue) pixels other than the pixel displaying red are respectively controlled to be in a white or black displaying state. Specifically, in this case, the three pixels may be placed in a displaying state of (red, white and white), (red, white and black) or (red, black and black). When displaying a green color or a blue color, the remaining two pixels other than the pixel of a target color (single color) to be displayed are similarly arranged to be in a white or black displaying state.
As a method to control the cell display state, a method (a vertical type) in which the particles are electrophoretically moved in a direction perpendicular to a substrate surface (in other words, in a direction along the observer's viewing direction) by electrodes provided on the substrates that hold the cells is known. Another known method is a method (a horizontal type) in which the particles are electrophoretically moved in a direction perpendicular to a surface of the partition wall (in other words, in a direction parallel with the substrate surface) by electrodes provided on the partition walls that divide the cells.
When particles charged in positive and negative opposite polarities are mixed in the cells, the particles of positive and negative opposite polarities (hereafter, simply referred to as “opposite polarities”) are mutually coupled in the process of electrophoresis of the particles in response to controlling of the display state (display color), which may cause aggregation and sedimentation of the particles, and lead to deterioration of the display performance of the EPD.